A Chimeric Subunit of Yeast Transcription Factor IIIC Forms a Subcomplex with τ95

ABSTRACT

The multisubunit yeast transcription factor IIIC (TFIIIC) is a multifunctional protein required for promoter recognition, transcription factor IIIB recruitment, and chromatin antirepression. We report the isolation and characterization of TFC7, an essential gene encoding the 55-kDa polypeptide, τ55, present in affinity-purified TFIIIC. τ55 is a chimeric protein generated by an ancient chromosomal rearrangement. Its C-terminal half is essential for cell viability and sufficient to ensure TFIIIC function in DNA binding and transcription assays. The N-terminal half is nonessential and highly similar to a putative yeast protein encoded on another chromosome and to a cyanobacterial protein of unknown function. Partial deletions of the N-terminal domain impaired τ55 function at a high temperature or in media containing glycerol or ethanol, suggesting a link between PolIII transcription and metabolic pathways. Interestingly, τ55 was found, together with TFIIIC subunit τ95, in a protein complex which was distinct from TFIIIC and which may play a role in the regulation of PolIII transcription, possibly in relation to cell metabolism.

ACKNOWLEDGMENTS

We thank Christophe Carles and Françoise Bouet for peptide sequence determination and Anny Ruet for help in raising rabbit polyclonal antibodies. We are grateful to Janine Huet and Emmanuel Favry for B", recombinant TBP, recombinant TFIIIB₇₀, and PolIII preparations. We thank Jochen Rüth and Geneviève Dujardin for helpful discussions and Cathy Jackson for improving the manuscript.

This work was supported by a grant from the European Union BIOTECH program (to A.S.). N.M. was supported by a fellowship from the French Ministère de l’Enseignement Supérieur et de la Recherche, and R.A. was supported by a P.F.I. postdoctoral fellowship from the Spanish Ministerio de Educación y Cultura.